This invention relates to tuyeres and more particularly relates to tuyeres having separate body and nose chambers whereby the latter is preferentially cooled.
Preferential cooling for the nose area of tuyeres in, for example, blast furnaces has for some years now been accepted as a pre-requisite for good preformance and long life in service. Such cooling is established by conducting the coolant directly to the nose chamber through a tube which extends through the rear (body) chamber and the coolant issues from the nose either via the rear chamber--in which case there is only one inlet and one outlet necessary--or through another tube which passes through the rear chamber in a like manner to the inlet--in which case the rear chamber is separately supplied with coolant necessitating two inlets and two outlets for the tuyere.
The latter design therefore embodies two independent liquid coolant circuits and where the external pipework permits of this design it is preferred.
Two methods of construction of tuyeres having separate body and nose chambers have primarily been used. In one a bent tube extends through the rear chamber and itself constitutes the nose chamber within the mass of copper (or other good conductivity material) which is cast around it; in the other a separate nose chamber is prefabricated and joined on to the main body section; e.g. by welding or brazing, this chamber being coupled into circuit by an inlet tube, or an inlet and an outlet tube (as appropriate), which extends through the rear chamber as before.
Tuyeres provided by either of these methods however have inherent problems detrimental to performance in service. With the cast-in tube there is difficulty in ensuring an adequate bond between the tube and the surrounding cast metal; voids are often produced in this region which adversely affect the heat transfer characteristics. With a pre-fabricated nose chamber doubts arise in the ability of welded or brazed joints to withstand the harsh operating conditions within the furnace and failures giving rise to leakage of coolant (water) are not unknown.
It is an object of this invention to provide an improved tuyere.